ElectronicsLabUser Posted March 26, 2022 Report Share Posted March 26, 2022 I need to design a buck converter with the following requirements, Input voltage 24V - 100V (2 - 10 Amps) and the output voltage shall be 12V (20 Amps). I started with the following circuit available in the net. The Diode, Inductor, Capacitor i have not yet selected, First question is how do i switch the MOSFET, do i need to interface a micro controller to calculate the duty cycle based on the output current, input voltage? I am new to hardware design. Please help. Quote Link to comment Share on other sites More sharing options...
HarryA Posted March 26, 2022 Report Share Posted March 26, 2022 There is a lot to designing a dc to dc buck converter. For example see: https://www.maximintegrated.com/en/design/technical-documents/tutorials/2/2031.html You can buy one for far less than the cost of the parts to build one. See: https://www.amazon.com/Aceirmc-Converter-Adjustable-Regulator-Protection/dp/B0823MM1DV/ref=sr_1_6?crid=1AB7YZ4O9O8B0 You may find complete circuits on the internet. The inductor is the tricky part . What to use as a core and how to wind it for 20 amperes. Quote Link to comment Share on other sites More sharing options...
ElectronicsLabUser Posted March 27, 2022 Author Report Share Posted March 27, 2022 Thank you for the reply, by help from other forums online i selected LTC3703 regulator, and from the application note in the data sheet https://pdf1.alldatasheet.com/datasheet-pdf/view/97352/LINER/LTC3703.html Can i use this circuit as is to meet the requirements i mentioned? I want current upto 10 Amps, can i change the circuit accordingly? Please advise. Quote Link to comment Share on other sites More sharing options...
HarryA Posted March 28, 2022 Report Share Posted March 28, 2022 As this chip is made by Analog and Analog owns LTspice simulator the circuit appears in the simulator and can be explored there. The circuit there is slightly different. Note it uses the FDS6680A mosfets. If you want 10 amperes make sure the mosfets can handle the current. Go here and put in your requirements then you will see some 10 ampere chips: https://www.analog.com/en/parametricsearch/11491#/p5573=min|24&p5574=100|max&p5347=min|12&p5357=12|max&p5349=10|240&qsfv=vinmin|24_vinmax|100_vout|12_iout|10&p5362=Buck ElectronicsLabUser 1 Quote Link to comment Share on other sites More sharing options...
ElectronicsLabUser Posted April 1, 2022 Author Report Share Posted April 1, 2022 On 3/28/2022 at 7:26 AM, HarryA said: The circuit there is slightly different. Note it uses the FDS6680A mosfets. On 3/28/2022 at 7:26 AM, HarryA said: I have started going through the data sheet and trying to download ltspice simulation models for buck converter, but the above circuit i could not locate, have you created on your own? just for information. Quote Link to comment Share on other sites More sharing options...
HarryA Posted April 1, 2022 Report Share Posted April 1, 2022 In LTspice on selecting components open the directory [Power Products] in the listing find LTC3705 when you click on it you will see "Open this macromodel's example circuit" that will display the circuit. You can select RUN and the output display will come up. You can poke around the circuit with the "red probe" and see the various wave forms are there. You may know this already but other reads may not. Perhaps if you click on some other types there you will find more converters of interest; as it displays a brief description of each. The Analog site listed above is is busted. I got in once but never again. But if you search on LTC3703 off that page you will get some links that look like they may be helpful. This link seems to work. Gets you to where you can enter you requirements. https://www.analog.com/en/product-category/step-down-buck-regulators.html Quote Link to comment Share on other sites More sharing options...
ElectronicsLabUser Posted April 4, 2022 Author Report Share Posted April 4, 2022 I saw the data sheet of the LTC3703 and there was a design example on page 27, i followed the same procedure. LTC3703 Data Sheet Specifications: VIN = 24V to 100V, VOUT = 12V, IOUT(Max) = 10A, f = 250kHz 1. RSET As per the formula in the data sheet RSET(kOhm) = 7100/(250 - 25) = 31.5KOhm -> eq1 2. Inductor value for about 40% ripple current at maximum VIN L = 12/250K*0.4*10(1 - 12/100) = 10.56uH. -> eq2 3. Minimum On-time ton(min) = 12/(100*250kHz) = 480nS -> eq3 which is above LTC3703's 200ns Minimum on-time. 4. Top and Bottom MOSFET switch Since the drain of each MOSFET will see the full supply voltage 100V (max) plus any ringing, choose a 125V MOSFET to provide a margin of safety. PMAIN = 1.32W -> eq4 = 96.4DegC. =1.84 -> eq5 TJ = 70 + 1.84*20 = 106.8 5. Current Limit Resistor RDS(ON) = (25mOhm)/2 [1 + 0.009(105 - 25)] = 21.5mOhm IMAX pin voltage = 10*0.0215 = 0.215V RMAX = 0.215/12uA = 18k -> eq6 6. CIN is chosen for an RMS current rating of 5A (IMAX/2) at 85DegC. 7. For the output capacitor 2 low ESR OS-CON capacitors (18mF) are used. The LTSPICE model is in progress, i have completed to the below level, the work is still in progress, i also need to choose the MOSFET. But based on the above steps, could you please provide comments. design.pdf Quote Link to comment Share on other sites More sharing options...
TiaPettit Posted May 27, 2022 Report Share Posted May 27, 2022 On 3/26/2022 at 8:08 PM, HarryA said: There is a lot to designing a dc to dc buck converter. For example see: https://www.maximintegrated.com/en/design/technical-documents/tutorials/2/2031.html You can buy one for far less than the cost of the parts to build one. See: https://www.amazon.com/Aceirmc-Converter-Adjustable-Regulator-Protection/dp/B0823MM1DV/ref=sr_1_6?crid=1AB7YZ4O9O8B0 You may find complete circuits on the internet. The inductor is the tricky part . What to use as a core and how to wind it for 20 amperes. Hello, thank you so much for those links. I am working on my college project and for that I need some help regarding DC to DC bulk converter. I am so glad I have found your post. I also found the MasterBundles website online where I have found a lot of templates that I can use for my website. Now, I don't have to waste my time making templates. Hello, thank you. Quote Link to comment Share on other sites More sharing options...
loribennms Posted October 13, 2022 Report Share Posted October 13, 2022 On 3/26/2022 at 1:17 PM, ElectronicsLabUser said: I need to design a buck converter with the following requirements, Input voltage 24V - 100V (2 - 10 Amps) and the output voltage shall be 12V (20 Amps). I started with the following circuit available in the net. The Diode, Inductor, Capacitor i have not yet selected, First question is how do i switch the MOSFET, do i need to interface a micro controller to calculate the duty cycle based on the output current, input voltage? I am new to hardware design. Please help. Web Designers in Charlotte Nc Then the best solution would be to check on manufacturer toolkits. TI, AD and practically any DCDC converter manufacturer has some kind of design toolkit: you give the parameters and get a design with calculated properties and a BOM. Quote Link to comment Share on other sites More sharing options...
loribennms Posted October 22, 2022 Report Share Posted October 22, 2022 On 3/27/2022 at 11:06 PM, ElectronicsLabUser said: Thank you for the reply, by help from other forums online i selected LTC3703 regulator, and from the application note in the data sheet https://pdf1.alldatasheet.com/datasheet-pdf/view/97352/LINER/LTC3703.html Can i use this circuit as is to meet the requirements i mentioned? I want current upto 10 Amps, can i change the circuit accordingly? Please advise. blackpods what did you say? Quote Link to comment Share on other sites More sharing options...
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